Cerebral obstructive diseases, moyamoya disease and the like caused by atherosclerosis in the cerebral artery often result in chronic reduction in cerebral blood flow. This state may lead not only to the subsequent cerebral ischemic events but also to neuropathological changes including dementia (Stroke 25:1022-1027, Stroke 29:1058-1062 (1998)); Stroke 24:259-264 (1993); Ann. N. Y. Acad. Sci. 695:190-193 (1993)). However, no effective methods for improving the reduced blood flow in these cerebrovascular disorders have been established yet. It is known that in ischemic attacks, active angiogenesis takes place specifically at the peripheral regions of the ischemia, and this is involved in prolonged survival in humans (Stroke 25:1794-1798 (1994)). Thus, angiogenesis has been considered to play an important role in recovery from cerebral ischemia and prevention of future attacks.
The development of new blood vessels and angiogenesis are triggered concurrently with the activation of the endothelial cell. A growth factor that has been shown not only to stimulate angiogenesis in vivo, but also to be mitogenic in vitro to the endothelial cell is called “angiogenic growth factor.”
The therapeutic involvement of angiogenic growth factor was first described in literature by Folkman et al. (N. Eng. J. Med. 285:1182-1186 (1971)). Subsequent research confirmed that recombinant angiogenic factor such as fibroblast growth factor (FGF) family (Science 257:1401-1403 (1992); Nature 362:844-846 (1993)), endothelial growth factor (J. Surg. Res. 54:575-583 (1993)), and vascular endothelial growth factor (VEGF) may be used to promote and/or enhance the development of collateral circulation shunt in animal models of myocardial and hindlimb ischemia (Circulation 90:II-228-II-234 (1994)). Furthermore, the present inventors have found that HGF acts as a endothelium-specific growth factor as does VEGF (J. Hypertens. 14:1067-1072 (1996)).
A strategy as described above that employs angiogenic growth factor to treat vascular disorders is called “therapeutic angiogenesis.” More recently, the strategy has been applied to ischemic diseases in humans. However, the effectiveness of the strategy in cerebral ischemia has not been known so far.
Hepatocyte growth factor (HGF) is a pleiotropic cytokine that exhibits mitogenic, motility promoting, and morphogenic activity on a variety of cells (Nature 342:440-443 (1989)).
Effects of HGF on the brain has been reported as follows. Thus, it is known that HGF in combination with c-Met/HGF receptor of a transmembrane tyrosine kinase is expressed at various regions in the brain, and the operative linkage of HGF and c-Met enhances the survival of neurons in the primary culture of hippocampus, and induces neutrite elongation in the development in vitro of neurons (J. Cell. Biol. 126:485-494 (1994); Japanese Unexamined Patent Publication (Kokai) No. 7-89869). Recently, it has been reported that HGF is induced in neurons in ischemia (Brain Res. 799:311-316 (1998)), that recombinant HGF has a neuroprotective effect on delayed neuronal death after ischemia in the hippocampus, and that the continuous injection of recombinant HGF into the brain was effective in reducing the size of infarction (J. Cereb. Blood Flow Metab. 18:345-348 (1998)). These findings suggest that HGF acts as an important neurotrophic factor in cerebral ischemia.
On the other hand, vascular endothelial growth factor (VEGF) is a dimeric glycoprotein mitogenic to the endothelial cell and has an ability of enhancing vascular permeability. VEGF has a direct and specific mitogenic effect on the endothelial cell (Biochem. Biophys. Res. Commun. 161:851-858 (1989)). The binding sites of VEGF including tyrosine kinase receptor Flt, Flk-1, and KDR occur on the endothelial cell but not on other cell types, thereby limiting the effect of VEGF to the endothelial cell.
With respect to the effect of VEGF on the brain, it has been reported that VEGF in the central nervous system is rapidly induced by ischemic disorders in the brain (Mol. Cell. Biol., 16:4604-4613 (1996)), and that the administration of recombinant VEGF to the brain surface effectively reduced the amount of infarction (J. Cereb. Blood Flow Metab. 18:887-895 (1998)). Details thereof has not been known, however.
In another aspect, in addition to the above-mentioned actions of HGF and VEGF, these factors are potent angiogenic growth factors as mentioned above (J. Cell. Biol. 119:629-641 (1992)); Biochem. Biophys. Res. Commun. 161:851-858 (1989)). Ischemic attacks are known to give rise to active angiogenesis in the periphery of ischemia, which is related to prolonged survival of humans (Stroke 25:1794-1798 (1994)). Thus, angiogenesis is thought to play an important role in recovery from cerebral ischemia and in prevention of future attacks. However, it is not known whether therapeutic angiogenesis using recombinant HGF or VEGF is actually feasible for cerebral ischemia etc. Furthermore, recombinant angiogenic growth factors rapidly disappear from the brain and thus require continuous injection into the brain, which procedure is rather dangerous and impractical in the clinical settings. Thus, it would be reasonable if the technique of gene introduction is used to express and secrete angiogenic growth factors in ischemic brain and its periphery on a continual basis. There are no examples so far in which HGF gene or VEGF gene has been applied (gene therapy) to ischemic disorders in the brain, and possibly because of its unique feature of the brain tissue, there are no suggestions made on the applicability thereof.